The Far Ultraviolet Spectral Signatures of Formaldehyde and Carbon Dioxide in Comets

Details The Far Ultraviolet Spectral Signatures of Formaldehyde and Carbon Dioxide in Comets The Far Ultraviolet Spectral Signatures of Formaldehyde and Carbon Dioxide in Comets

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.2006f&link_type=abstract

American Astronomical Society, DPS meeting #38, #20.06; Bulletin of the American Astronomical Society, Vol. 38, p.517

Astronomy and Astrophysics

Astronomy

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Scientific paper

Observations of four comets made with the Far Ultraviolet Spectroscopic Explorer show the rotational envelope of the (0,0) band of the CO Hopfield-Birge system (C 1Σ+ - X 1Σ+) at 1088 Å to consist of both "cold” and "hot” components, the "cold” component accounting for 75% of the flux and with a rotational temperature in the range 55 - 75 K. We identify the rotationally "hot” component (T 500 K) as coming from the dissociation of CO2 into CO, with electron impact dissociation and photodissociation contributing roughly equally. An additional weak, broad satellite band is seen centered near the position of the P(40) line that we attribute to CO fluorescence from a non-thermal high J rotational population produced by photodissociation of formaldehyde into CO and H2. This process, well studied in the laboratory, also leaves the H2 preferentially populated in excited vibrational levels that are identified by fluorescent H2 lines in the spectrum excited by solar O VI λ1031.9. Electron impact excitation of CO, rather than resonance fluorescence, is the primary source of the observed B 1Σ+ - X 1Σ+ (0,0) band at 1151 Å.
Financial support was provided by NASA contract NAS5-32985 and NASA grant NAG5-12963.

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